Dual frequency antenna feed is required in many antenna systems. With dual frequency feed, a single antenna can be used for simultaneous transmitting and receiving, provided that the frequency separatio nis adequate. Alternatively, a separate communications link may be established on the other frequency.
In the prior art, various forms of dual feeders, alsoo known as diplexers, have been used for combining transmit and receive signals in a sinngle antenna. However, these have generally been quite bulky and heavy. Furthermore, for signals that are widely separated in frequency, conventional diplexers are difficult to construct due to the limitations of waveguide design. If the waveguide at the common port is large enough to carry the dominant propagation mode for the lower frequency, it will often be the case that it will be too large to prevent the propagation of undesired higher order modes of the higher frequency signal.
A further limitation in many designs is that they are not easily adapted to circular polarization.
Accordingly, it is an object of the present invention to provide a dual frequency antenna feed or launcher that is compatible with circular polarization.
It is yet another object to provide a dual frequency launcher that is compact and light.
It is yet another object of this invention to provide a dual frequency launcher that does not promote the propagation of undesired waveguide modes at the higher frequency.
These and other objects are obtained in an antenna launcher containing a first central, circular waveguide suitable for use at one frequency, around the axis of which exist a plurality of annular filter cavities tuned to a second frequency, and into which cavities, energy of the second frequency is introduced or withdrawn.